Flexible magnetic recording disks or diskettes, e.g., "floppy disks", are typically permanently encased in plastic jackets made from, e.g., polyvinyl chloride or polyester, and having a nonabrasive liner. Because these flexible disks are susceptible to exposure to magnetic fields or static electricity, dust and dirt, and are sensitive to pressure caused by, for example, a writing instrument, they are typically stored in protective storage envelopes when not in use in order to preserve the reproducibility of the information stored thereon. Warnings and directions relative to proper use of the diskette as well as promotional information are typically printed on the envelope.
Storage envelopes currently on the market typically comprise a rear wall and a front wall joined together at the bottom and two opposite sides to form an open pocket, which is dimensioned to receive the diskette as shown in the drawing. The height of the rear wall may be greater than that of the front wall so that it extends beyond the opening of the pocket, thereby facilitating the easy insertion into and removal from the envelope of the diskette. The depth of the pocket formed by joining the rear and front walls of the protective envelope is usually equal to about 2/3 to 3/4 the height of the diskette so that the openings in the diskette jacket, e.g., central hole, index hole, and head access slot, are covered. U.S. Pat. No. 4,473,153 (Colangelo), discloses a somewhat similar protective envelope which further comprises a cover pivotally joined to the top edge of the rear wall. The cover may be pivoted between an open position to allow insertion of the diskette into, and removal from, the envelope and a closed position to enclose the entire diskette within the envelope.
Dust or dirt particles may interfere with the diskette mechanism or read/record apparatus leading to interference with or loss of recorded information, particularly with high density recording media, therefore storaqe envelopes should preferably be designed to minimize the dirt conditions to which the diskette is subjected. In this regard, storage envelopes should be made from a material generating a low amount of debris. During use, e.g., when slid into and out of the storage envelope, recording diskettes tend to accumulate a static charge on themselves and the envelope, therefore, the storage envelope is preferably made from a material having a rapid static decay rate in order to dissipate accumulated static charges thereby reducing the likelihood of attracting dirt and debris particles. For instance, the envelope should preferably dissipate ninety percent of a 5000 volt charge in a one-half second or less according to the conditions in Method 4046 of Federal Test Method Std. No. 101B. Magnetic recording diskettes are transported, used, and stored throughout ambient temperature and humidity conditions which may range from 50.degree. F. to 140.degree. F. (10.degree. C. to 60.degree. C.) and from nearly 0 percent relative humidity to about 80 percent relative humidity and it is desirable for storage envelopes to retain their shape throughout such conditions, i.e., exhibit dimensional stability, without tending to warp or pillow. Preferably, storage envelopes should be made from a durable sheet material having a tensile strength of about 25.0 pounds per inch width (45.0 Newtons per centimeter width) or more and an Elmendorf Tear value of about 100 grams or more in order to withstand normal wear and tear. It is desirable, both for aesthetic value and for proper operation of automatic insertion equipment, for the storage envelopes to be made from a material having a Taber Stiffness of between about 1 and 7 Taber units.
Storage envelopes for recording diskettes are currently made from a variety of materials as disclosed in U.S. Pat. No. 4,473,153. Examples thereof include coated or uncoated papers, or polymeric materials such as polyvinyls and polyolefins. Insofar as known, no presently used material provides, at the same time, the low level of debris generation, rapid static decay rate, high stiffness and dimensional stability, and easy convertability and printability which is desired for diskette storage envelopes. For instance, although it is a commonly used material, solid bleached sulphate ("SBS") paper, e.g., 8 point clay coated SBS, Which is commercially available from a number of manufacturers, has a relatively slow static decay rate and a high rate of debris generation, each of which may lead to interference with or loss of recorded information. Further, this material has poor dimensional stability and is typically adversely affected by high humidity conditions, e.g., storage envelopes made therefrom tend to warp and pillow as the paper absorbs moisture and expands. Another commonly used material, TYVEK, a spunbonded polyethylene available from E.I. duPont de Nemours & Company, is well known for the low level of debris which it generates, but does not provide satisfactory stiffness at economical thicknesses, e.g., it has a Taber Stiffness of only about 0.8 to about 1.4 Taber unit at a thickness of about 7.2 mils (180 microns), and does not have as uniform a surface as desired for optimum printing quality. Further, TYVEK does not have as fast a rate of static decay as is desired to minimize attraction of debris.